bubbles in the paint on rear sill

[Smithy]

Yesterday I noticed some bubbles in the paint right by the ns rear sill when I was washing my 2. I guess I need to look a little deeper as to what's going on. I'm thinking its not far from the drain hole so I wonder if water is getting trapped? But I do keep the drains clear and its a little bit back from there. Can anyone suggest a next step? maybe strip it back treat and repaint?

[Carolyn]

It pays to remove the wheel arch liner once a year and shift the accumulation of crud that gets behind the bottom of the wing.  It's a spot where rust can get started. 

Edit:  You may have to sand the paint back, fill any holes/blemishes and re-paint.  I suspect it will have rusted through from behind.

[Smithy]

Thanks Carolyn I will have a look.

[Newbie57]

My off side is the same. It's very corroded on the inside. As a holding measure I cleared out the loose rust and applied hammerite. Since then I bought a replacement wing. Just not fitted it yet.